Automated fabrication of corrugated paper products

ABSTRACT

Method and equipment for the manufacture of corrugated paper products includes separate heaters for preparing liner and medium components. Data regarding these components is collected and an optimum conditioning for the components is determined.

This is a division, of application Ser. No. 08/432,038, filed May 1,1995, now U.S. Patent pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to the production of corrugated paper products,and particularly corrugated board.

2. Description of Related Art:

Sheets of corrugated board may be used for many purposes whereprotection, separation, or support is required. A corrugated medium istypically formed in a machine which moistens or steams a paper web priorto passing it between two metal rollers cut with alternate flute tipsand grooves which are geared to run in complement to each other. Thisimpresses permanent parallel flutes in the paper perpendicularly to themachine direction. The flutes contribute significant rigidity andresistance to products which utilize the resulting corrugated medium.

After a corrugated medium is formed, it may be pasted or otherwisemounted to a liner to produce single-faced corrugated board. If linersare joined to both sides of the corrugated material, a double-wallcorrugated board results, and if double-faced and single-faced board arejoined together, a double-wall board results.

The economic impetus to produce corrugated board in mass quantities hasled to the development of an in-line production process forsingle-faced, double-faced and double-wall corrugated board. The in-lineproduction processes have several constituent steps, including specificsteps for monitoring and adjusting the temperature and moisture contentsof the paper webs employed. The ability to accurately monitor andcontrol the various constituent steps involved in the in-line processescan yield substantial economic benefits for the manufacturer and improvequality control.

The many operational steps employed in a commercial process areinterdependent, and any one constituent step may result in a variety ofdistinct undesirable qualities in the final product, and oftentimes itis difficult and time-consuming to isolate the root cause of a defect inthe product based merely upon routine observation of the defect.Nevertheless, machine operators have been relied on to make adjustmentsto these types of machines in response to observations of identifiabledefects or sets of defects, based on the operator's intuition orexperience.

Typically, adjustments to the machine are made in iterative steps. This,of course, results in waste of not only paper and adhesive, but also inlost production time. It has been observed that perceived acceptableoperating conditions lie within a fairly sizeable range of operatingconditions, and a rapid determination of a narrower, more accurateoperating range of conditions has been sought.

The principal control steps for operating machines making corrugatedpaper board focuses on the steps of preparing a liner for adhesivejoinder, and a substantially different preparation of a paper web forformation into a corrugated medium. While the equipment for performingthese different steps bears some similarity, it has been recognized thatsubstantially different operating principles are needed if commerciallyacceptable products are to be made on a consistent, cost effectivebasis.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide improved methods forpreparing paper liners for adhesive joinder in the manufacturing ofcorrugated board.

Another object of the present invention is to provide improved methodsfor preparing paper webs for formation into a corrugated medium.

Another object of the present invention is to provide improved methodsfor adhesively joining a liner to a medium.

Yet another object of the present invention is to provide improvedcontrols for the automated manufacture of corrugated board comprisingone or more liners and layers of paper medium, adhesively joinedtogether.

These and other objects according to principles of the present inventionare provided in a method for preparing a paper web for adhesive joinder,comprising the steps of:

providing a paper web having first and second opposed surfaces andcontaining moisture;

providing heating means with a curved outer heated surface;

providing a wrap arm for wrapping the paper web across the heatingmeans, with the wrap arm movable between different positions so as tobring greater and lesser portions of the paper web in contact with theheating means;

moving the wrap arm between different positions so as to bring achanging amount of the first surface of the paper web in contact withthe heating means;

sensing, for the different positions of the wrap arm, the surfacemoisture carried by the paper web at the first surface and thetemperature of the paper web at the first surface;

determining a low temperature wrap arm position at which a rate ofincrease of surface moisture increases;

determining a high temperature wrap arm position at which a rate ofincrease of surface temperature is negligible;

determining an offset comprising the difference between the lowtemperature wrap arm position and the high temperature wrap armposition;

determining a high moisture wrap arm position at which a rate ofincrease of surface moisture is negligible;

determining a desired operating position of the wrap arm by adjustingthe high moisture wrap arm position toward the low temperature wrap armposition by an amount corresponding to the offset; and

moving the wrap arm to the desired operating position.

Other objects of the present invention are provided in a method forpreparing a paper web for corrugation, comprising the steps of:

providing a paper web having first and second opposed major surfaces andcontaining moisture;

providing heating means with a curved outer heated surface;

providing a wrap arm for wrapping the paper web across the heatingmeans, with the wrap arm movable between maximum and minimum positionsso as to bring greater and lesser portions of the paper web in contactwith the heating means;

moving the wrap arm between a series of different positions, betweenmaximum and minimum positions so as to bring a changing amount of thefirst surface of the paper web in contact with the heating means;

sensing, for the different positions of the wrap arm, and the moistureof the paper web;

determining a low moisture wrap arm position at which a rate of increaseof moisture increases;

determining a high moisture wrap arm position at which a rate ofincrease of web moisture is negligible;

determining an offset comprising one-half of the difference between thelow moisture wrap arm position and the high moisture wrap arm position;

determining a desired operating position of the wrap arm by adjustingthe high moisture wrap arm position toward the low moisture wrap armposition by an amount corresponding to the offset; and

moving the wrap arm to the desired operating position.

Further objects of the present invention are provided in preparing apaper web for adhesive joinder in accordance with the above, preparing apaper web for corrugation in accordance with the above, applying acoating of adhesive between the two, and pressing the two together.

Other objects of the present invention are provided in a method ofjoining a paper liner to a medium comprising a corrugated paper web,comprising the steps of:

a) forming the liner from a paper web in preparation for adhesivejoinder to the medium, comprising the steps of:

providing a paper web having first and second opposed major surfaces andcontaining moisture;

providing a heater with a curved outer heated surface;

providing a liner wrap arm for wrapping the paper web across the curvedouter heated surface, with the liner wrap arm movable between first andsecond positions so as to bring greater and lesser portions of the paperweb in contact with the curved outer heated surface;

moving the liner wrap arm between said first and said second positionsso as to bring a changing amount of the first surface of the paper webin contact with the curved outer heated surface;

sensing, for the different positions of the liner wrap arm, the surfacemoisture carried by the paper web at the first surface and thetemperature of the paper web at the first surface;

determining a low temperature liner wrap arm position at which a rate ofincrease of surface moisture increases;

determining a high temperature liner wrap arm position at which a rateof increase of surface temperature is negligible;

determining an offset comprising the difference between the lowtemperature liner wrap arm position and the high temperature liner wraparm position;

determining a high moisture liner wrap arm position at which a rate ofincrease of surface moisture is negligible;

determining a desired operating position of the liner wrap arm byadjusting the high moisture liner wrap arm position toward the lowtemperature liner wrap arm position by an amount corresponding to theoffset; and

moving the liner wrap arm to the desired operating position;

b) forming the medium from another paper web in preparation for adhesivejoinder to the liner, comprising the steps of:

providing another paper web having first and second opposed majorsurfaces and containing moisture;

providing a medium heater with a curved outer heated surface; providinga medium wrap arm for wrapping the paper web across the curved outerheated surface, with the medium wrap arm movable between maximum andminimum positions so as to bring greater and lesser portions of thepaper web in contact with the curved outer heated surface of the mediumheater;

moving the medium wrap arm between a series of different positions,between said maximum and said minimum positions so as to bring achanging amount of the first surface of the paper web in contact withthe curved outer heated surface of the medium heater;

sensing, for the different positions of the medium wrap arm, themoisture of the paper web;

determining a low moisture medium wrap arm position at which a rate ofincrease of moisture increases;

determining a high moisture medium wrap arm position at which a rate ofincrease of web moisture is negligible;

determining an offset comprising one-half of the difference between thelow moisture medium wrap arm position and the high moisture medium wraparm position;

determining a desired operating position of the medium wrap arm byadjusting the high moisture medium wrap arm position toward the lowmoisture medium wrap arm position by an amount corresponding to theoffset; and

moving the medium wrap arm to the desired operating position;

c) coating one of said liner and said medium with an adhesive; and

pressing said liner and said medium together.

In accordance with the present invention, there is provided anelectronic or other type of control system for automatically regulatingquality in a process for manufacturing corrugated board. In one aspect,the present invention employs a high-speed computer for system control.The computer is in communication with a plurality of sensors which areplaced in various relevant locations throughout the system. The sensorsmay include moisture sensors, thermometers, speed sensors, positionsensors, buttons and similar devices. The sensors continuously relayinformation that the computer uses to evaluate the condition of thesystem. The computer then effects changes in the system, when necessary,through a number of actuators. Actuators may include wrap arm control,roller pressure, valves, lights, thermostats and the like.

The control system in accordance with the invention enables theimplementation of corrective adjustments based upon objective, in-linecriteria rather than upon a subjective evaluation of a finished productby an operator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a machine for the manufacture ofsingle-faced corrugated board in accordance with the process of theinvention;

FIG. 2 is a perspective view of a single-faced corrugated board producedby apparatus in accordance with the invention;

FIGS. 3a and 3b show a schematic side view of a machine for themanufacture of double-wall corrugated board in accordance with theprocess of the invention;

FIG. 4 is a perspective view of a double-wall corrugated board producedby apparatus in accordance with the invention;

FIG. 5 is a schematic diagram of a heating means employed in thepractice of the present invention;

FIG. 6 is a diagram indicating operation of the heating means of FIG. 5;

FIG. 7 is a schematic diagram of another heating means employed in thepractice of the present invention;

FIG. 8 is a diagram indicating operation of the heating means of FIG. 7;

FIGS. 9a and 9b together show a flow chart indicating control of theheating means of FIG. 5; and

FIGS. 10a and 10b together comprise a flow chart indicating control ofthe heating means of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As will be seen herein, the present invention contemplates themanufacture of various paperboard products, including single-facedcorrugated board as well as products such as double-faced corrugatedboard and double-wall corrugated board which employ a single-facedcorrugated board as a component. It has been found advantageous in amanufacturing environment to employ a separate in-line manufacturingmachine for producing single-faced board, and for providing separateautomated in-line machinery for producing other corrugated boards,employing single-faced corrugated board as a component.

Single-Faced Board Manufacture

Turning now to FIGS. 1 and 2, an improved manufacturing apparatus 5 andrelated method is provided for the manufacture of single-facedcorrugated board. The improvements are directed to the automated controlof certain parameters of manufacture based on objective, substantiallycontinuous sensor readings along in-line manufacturing apparatus. Thein-line manufacturing apparatus 5 for manufacturing single-facedcorrugated board includes roll stands 12 which retain rolled webs 18 ofliner 11 for payout as the rolled webs 18 are rotated on the stand 12.One rolled web is employed at a time. The stand 12 has a skew adjustment16 to properly align the liner 11 as it is spun off the web roll 18, andthe stand 12 has a brake 14 to adjust the tension of the liner 11 as itis fed into a splicer 19. The splicer 19 also has a tension adjustment20.

After passing through a series of rollers, including roller 338, theliner 11 is wrapped around the outer curved surface 302 of asubstantially cylindrical preheater 24. The heat and pressure applied tothe wrapped portion causes moisture from the interior of the liner 11 tomove toward the surface of the liner. The amount of wrap, i.e., theangular extent of contact between the liner 11 and the outer, heatedsurface of preheater 24, is actuated by a preheater wrap arm 22 whichmoves across the outer preheater surface to adjust the amount or angleof contact. The preheater 24 also has a brake 26 to adjust the amount oftension in the liner 11.

As shown in FIG. 1, liner 11 is wrapped around the lower left part ofpreheater 24. If desired, liner 11 could also be wrapped around theupper right part of preheater 24, so as to treat the opposite majorsurface of liner 11. In this latter arrangement, liner 11 would passover the left hand end of wrap arm 22, with counterclockwise movement ofwrap arm 22 causing a greater amount of wrap. However, according to oneaspect of the present invention, whichever surface of the liner contactspreheater 24, the surface of liner to be monitored for calculation of anoptimum wrap arm position is the surface at which an adhesive bond is tobe formed.

After being wrapped, the liner passes a surface moisture sensor 27 tomeasure the surface moisture on the liner 11 and to relay accumulateddata through conductors to an electronic controller EC. In order toproperly form the single-faced corrugated board (and corrugated productsemploying this board), it is critical that there be neither too much nortoo little moisture on the surface of the liner 11. In addition towarping, improper levels of moisture may also contribute to poorsubsequent adhesion between the liner and a corrugated medium 31.Shortly after passing the moisture sensor 27, the liner 11 passes atemperature sensor 29 which also relays information to the electroniccontroller EC. The liner 11 is then ready for mounting to corrugatedmedium.

The pre-corrugation steps for the preparation of paper web comprisingmedium 31 are to some extent similar to those for preparing the liner 11for mounting. There is a rolled web 36 which rotates on a roll stand 30.A skew adjustment on the stand 30 keeps the medium 31 properly orientedand a brake 32 controls the tension in the medium 31. The medium is alsorun through a splicer 37 which has a tension adjustment 38.

The medium 31 is then wrapped around the outer surface of asubstantially cylindrical preconditioner 42. Heat and pressure areapplied to the wrapped portion of the medium to cause moisture withinthe medium to more evenly distribute throughout the thickness of themedium. If necessary, additional moisture can be added to the surface ofthe medium 31 at the beginning of the wrap by a preconditioning steamer44. The amount of wrap, i.e., the angular extent of contact between themedium 31 and the heated outer surface of preconditioner 42 is actuatedby a wrap arm 40 which moves across the outer surface of the preheaterto adjust the amount of contact.

An interior or averaging type of moisture sensor 45 detects the moisturein the paper web 31 and sends a signal indicative of the moisturereading to electronic controller EC. In addition to warping, improperlevels of moisture in a medium 31 may also contribute to impropershaping and size of the corrugated medium, and may also contribute toimproper adhesion of the corrugated medium to liner 11, and other paperboard that it may be combined with. Unlike the conditioning of the liner11, which utilizes moisture value at the surface of the paper web, ithas been found that better results are achieved at the mediumpreconditioner 42, if internal, average moisture values are measured.

Generally speaking, the medium 31 is wrapped around the upper art ofpreconditioner 42. However, if desired, medium 31 could be wrappedaround the lower half of preconditioner 42, passing over the left handside of wrap arm 40 shown in FIG. 1. While in many instances it may bepreferred that the surface of medium 31 to be conditioned by contactwith preconditioner 42 is that surface which later receives an adhesivecoating, either surface of the preconditioned medium may be monitored,since it is the internal moisture value rather than the surface moisturevalue which is important.

The medium 31 then begins the corrugation process, passing a mediumspreader bar 46, with an adjustment mechanism, to achieve a more uniformtension in the medium 31. The medium then passes through optionalshowers 48 and 50, and an oil mist applicator 66. The medium 31 windsaround an upper corrugator roll 56, comprising an alternately ridged andgrooved roller. The medium 31 passes between the upper corrugator roll56 and a lower corrugator roll 54 which is also alternately ridged andgrooved so that it generally rolls in complementary surface contact withthe upper corrugator roll 56. As the medium 31 passes between the tworolls 54 and 56, the alternatingly ridged and grooved surfaces form theparallel flutes in the medium 31 (FIG. 2). The pressure of the surfacecontact between the two rolls is adjustable since inadequate pressureyields poor flute formation while excessive pressure may damage, or evencompletely sever, the medium 31. The corrugator rolls 54, 56 cooperateso as to impart a continuous wave shape which is visible, for example,in FIG. 2. If the paper web comprising medium 31 is not properlypreconditioned, it is likely that medium 31 will not have the desiredshape after passing through the corrugator rolls 54, 56. Furtherinformation concerning the proper preconditioning of the paper webcomprising medium 31 will be given hereinafter.

As the medium 31 exits the corrugator rolls 54, 56, it passes through anip between roll 54 and a glue roll 58. The glue roll applies anadhesive film, such as, but not limited to, a starch product, to oneside of the corrugated medium 31, covering primarily only the flute tipson that side. Referring to FIG. 1, the corrugated medium 31, havinginside and outside surfaces, 13 and 15 respectively, is glued at itsinner tips 17 to the inside surface 21 of the liner 11 (i.e., thatportion of corrugated web 31 in contact with liner 11, as can be seen inFIG. 2). The glue roll 58 is located in a glue pan 61 having a glue pandam adjustment. Adhesive in the glue pan is carried by the glue roll 58and is smoothed into a controlled film by a wiper roll 60 which forms anip for the film with the glue roll 58. Along side the wiper roll 60 isa wiper blade 63 which has an adjustment mechanism to regulate thethickness of the film of adhesive.

The corrugated medium 31 and the liner 11 are then pulled togetherbetween the pressure roll 52 and the lower corrugator roll 54, where theadhesive-covered flutes of the corrugated medium 31 are pressed againstthe liner 11, bonding linearly along each flute. The operating speed ofthe manufacturing apparatus 5 is displayed by an operating speedindicator 68, which is coupled through a speed controller 69 toelectronic controller EC. The speed controller 69 is coupled to thedrives (not shown) for the corrugator rolls 54, 56 and pressure roll 52to control the rates of speed of the webs passing through themanufacturing apparatus 5. The resultant product is single-facedcorrugated board 10, as seen in FIG. 2, which may be used as such orincorporated into the manufacture of double-faced or double-wallcorrugated board or other paper products.

Double-wall Corrugated Board Manufacture

Double-wall corrugated board, indicated at 110 in FIG. 4, ismanufactured by mounting a top single-faced corrugated board 153 to amiddle single-faced corrugated board 131 so that the tips 117 of the topboard 153 adhere to the liner of the middle board 131. The middle board131 is mounted, at its tips 123 to a liner 121. Thus, each liner isseparated by a corrugated medium as shown in FIG. 4. Attention will nowbe directed to the double-backer assembly apparatus shown in FIGS. 3a,3b.

As in the manufacture of single-faced board, there is a liner 121, spunfrom a web 118 which rotates on a roll stand 112 having a brake 114 anda skew adjustment 116. The skew adjustment 116 controls the orientationof the web 118 and the brake 114 adjusts the tension in the liner 121.Also affecting this tension is an adjustment mechanism 120 on thesplicer 119.

The liner gets wrapped around part of the perimeter of a substantiallycylindrical preheater 124. The heat and pressure of the wrap causes someof the moisture in the liner 121 onto the surface of the liner 121. Theamount of wrap, i.e., the angular extent of contact between the liner121 and the preheater 124, is controlled by a preheater wrap arm 122which moves to adjust the amount of contact. The preheater 124 also hasa brake 126 to adjust the amount of tension in the liner 121.

After being wrapped, the liner 121 passes a moisture sensor 127 tomeasure the amount of surface moisture on the liner 121 and to relayaccumulated data to the electronic controller EC through conductors (notshown). In order to properly form the double-faced corrugated board, itis critical that there be neither too much nor too little moisture onthe surface of the liner 121. Shortly after passing the moisture sensor127, the liner 121 passes a temperature sensor 128 which also relaysinformation to the electronic controller EC through conductors (notshown). The liner 121 is then prepared for mounting.

As illustrated in FIG. 3a, double-wall board has, in addition to theliner 121, two pre-formed single-faced corrugated boards, 131 and 153,constructed as explained above with reference to FIGS. 1 and 2. Theheight and "pitch" of the flutes of the corrugated boards 131 and 153need not be identical. For example, the flutes of one corrugated boardcould be higher or lower than the flutes of the other corrugated board.Further, it should be realized that the corrugated board 153 could beomitted, to form a double-faced board from the joinder of corrugatedboard 131 and liner 121.

The inner board 131 passes over a bridge guide unit 133 having a guideadjustment to control lateral displacement of the board 131 and a brake132 to keep the single-faced board 131 in line with the liner 121 and toinsure that a consistent amount of board 131 is drawn over a given timeperiod. The board 131 then passes an optional water spray 134, which maybe employed in some instances to help in reducing subsequent warpproblems.

The board 131 then gets wrapped around part of the perimeter of asubstantially cylindrical preheater 138. The heat and pressure of thewrap forces some of the moisture in the board 131 onto its surface. Theamount of wrap, as determined by the angular extent of contact betweenthe board 131 and the substantially circular preheater 138, is actuatedby a preheater wrap arm 136 which moves to adjust the amount of contact.The preheater 138 also has a brake 140 to adjust the amount of tensionin the board 131. After being wrapped, the board 131 passes a moisturesensor 141 to measure the amount of surface moisture on the board 131and to relay accumulated data through wires (not shown) to theelectronic controller EC. In order to properly form the double-facedcorrugated board, it is critical that there be neither too much nor toolittle moisture on the surface of the board 131. Shortly after passingthe moisture sensor 141, the board 131 passes a temperature sensor 143which also relays information to the electronic controller EC throughwires (not shown).

The board 131 continues its in-line progression, passing through asurface contact point between a rider roll 150 and a glue roll 142. Theglue roll 142 applies an adhesive film to the corrugated side of board131, covering primarily only the flute tips on that side. Part of theglue roll 142 is submerged in adhesive which sits in a glue pan 145. Theadhesive sticks to the glue roll 142 and is smoothed into a film by awiper roll 144. Alongside the wiper roll 144 is a wiper blade 147.Optional sensors 149, 151 may be employed to double-check the moisturecontent or other physical properties of the intermediate product.

The outer board 153 passes over a bridge guide unit 152 having a guideadjustment to control lateral displacement of the board 153 and a brake154 to keep the single-faced board 153 in line with the liner 121 and toinsure that a consistent amount of board 153 is drawn. The board 153then passes a water spray 156 designed to help in reducing subsequentwarp problems.

The board 153 then gets wrapped around part of the perimeter of anoptional substantially cylindrical preheater 157. The amount of wrap,the angular extent of contact between the board 153 and thesubstantially circular preheater 157, is actuated by a preheater wraparm 158 which moves across the preheated surface in the plane of thein-line process to adjust the amount of contact. The preheater 157 alsohas a brake 159 to adjust the amount of tension in the board 153.

After being wrapped, the board 153 passes a moisture sensor 161 tomeasure the amount of moisture and to relay accumulated data to theelectronic controller EC. Shortly after passing the moisture sensor 161,the board 153 passes a temperature sensor 163 which also relaysinformation to the electronic controller EC.

The board 153 then passes through a nip between a rider roll 170 and aglue roll 162. The glue roll 162 applies an adhesive film to thecorrugated side of the board 153, covering primarily only the flute tipson that side. Part of the glue roll 162 is submerged in the adhesivewhich sits in a glue pan 165. The adhesive sticks to the glue roll 162and is smoothed into a film by a wiper roll 164. Along side the wiperroll 164 is a wiper blade 167. After passing an optional steam shower172, the outer board 153 is ready for mounting. Optional sensors 169,171 may be employed to monitor physical properties of the intermediateproduct, if desired.

The liner 121, the inner single-faced corrugated board 131, and theouter single-faced corrugated board 153 are brought together along amachine 179 riding atop a hot plate table 173. The speed of thedouble-backer and the machine 179 are displayed by an operating speedindicator 182. The adhesive film on the corrugated side of the outerboard 153 adheres to the liner side of the inner board 131 while theadhesive film on the corrugated side of the inner board 131 adheres tothe liner 121. To strengthen the bonds and to form the double-wallcorrugated board 110, pressure is applied by a series of hold-downdevices 174 which exert force upon the board 110 as it passes.Simultaneously, the board 110 can be lifted by machine risers 178enabling it to pass slightly above the hot plates 177 (which areenergized by heat source 176) when operation of the manufacturingapparatus is temporarily halted.

In the preferred embodiment of the invention, there are fan blowers 180for reducing warp in lighter classifications of board and for decreasingor eliminating the formation of brittle board. To avoid slippage of themachine, there is a machine tension adjustment 184 near the back of thehot plate table 174.

The board 110 is then driven across traction section rollers 186 untilit passes a sensor 187 for detecting product. In the preferredembodiment, an anti-skid coating may then be applied by an anti-skidcoating applicator 188 in order to meet the special needs of aparticular use.

The board 110 subsequently encounters a slitter 189, having a slitterknife arrangement 190 with a lateral adjustment mechanism 192 whichcontrols a horizontal score alignment 194 and a vertical score alignment196. The board 110 is then pulled through a cutter 197 by knife feedrolls 198 which subsequently eject the freshly cut boards 110 throughsandwich machines 200.

Finally, the cut boards 110 exit the cutter 197 onto an upwardlyinclined downstacker machine 201, where, after being rolled under asnubber roll 202 while riding up the machine 201, they are stacked upagainst a substantially vertical backstop 206 emanating from downstackerrollers 208 beneath the stack. A machine speed adjustment 204 controlsthe rate at which the boards 110 are stacked.

Although double-wall products have been described, the present inventionalso contemplates manufacture of triple-wall and other multiple-wallproducts as well.

Preheater Control System

Referring now to FIGS. 5 and 6, operation of the preheater controls willbe described in greater detail. FIG. 5 shows preheater 24 with wrap arm22 located in a representative optimum running position. A stationaryguide roller 300 guides web 11 leaving the preheater stage, on its waytoward travel over pressure roller 52, in preparation for an adhesivejoining operation. As mentioned above, wrap arm 22 is movable, beingmounted for rotation about the outer surface 302 of preheater 24.

Outer surface 302, as mentioned, is preferably of a cylindrical shape,but may alternatively comprise virtually any curved shape as may bedesired. In the preferred embodiment, wrap arm 22 is mounted formovement so as to be kept at a constant distance from outer surface 302,although this is not necessary. For example, outer surface 302 could, incross section, have an arcuate shape which need not be circular. Thewrap arm 22 would be mounted for movement across the outer surface withthe distance between the wrap arm and the outer surface, generallyspeaking, not being critical, since the wrap arm functions as a"lead-in" point for guiding incoming web material.

In the preferred embodiment, wrap arm 22 is movable between a minimum(unwrapped) position 308 and a maximum (fully wrapped) position 310. Inpractice, it has not been found unnecessary to move the wrap arm 22fully to the minimum position 308. Rather, it has been found sufficientto move the wrap arm 22 to a "park" position 312 indicated in FIG. 5. Asindicated in FIG. 5, the representative, or typical optimum operatingposition 314 lies between the full wrap position 310 and the parkposition 312.

Determination of the optimum operating position 314 will now bedescribed, with additional reference to FIG. 6. Initially, the wrap arm22 is moved to the full wrap, maximum position 310 and data collectionwithin the electronic controller EC is made ready. Moisture andtemperature readings are then taken from sensors 27, 29 as the wrap armis moved from the maximum wrap position 310 to the minimum wrap or parkposition 312, and moisture and temperature data is stored for angularpositions φ of the wrap arm 22.

Starting at the left hand end of FIG. 6, moisture data is collected atthe full wrap position. As the wrap arm 22 is moved to the position, themoisture curve 330 is generated toward the right hand end of FIG. 6.With continued movement of the wrap arm 22, moisture detected by sensor27 (see FIG. 1) increases, passing through a "knee" in curve 331identified by the reference numeral 334. With continued movement of wraparm 22 toward the park position, the moisture curve 330 rises to amaximum position 332 at which the rate of rise of moisture increase isnegligible, i.e., passes through a zero slope point. With furthermovement of the wrap arm 22 toward the park position 312 (see FIG. 5),moisture level in the paper medium drops (see position φ₀).

As the wrap arm travels toward point φ₁ (corresponding to the negligiblerate of increase point 332 on curve 330) from point φ₂ (corresponding todata point 334 on curve 330), temperature data shown in FIG. 6 as curve342 is collected. The point 346, the maximum point on curve 342, isnoted at position φ₃, corresponding to a negligible rate of increase oftemperature in the paper web. The moisture value 350 corresponding towrap arm position φ₃ can be determined from curve 330.

The angular displacement δ_(x), that is, the difference between wrap armpositions φ₃ and φ₂ is calculated as an offset value. As mentionedabove, wrap arm position φ₁ is noted as the maximum moisture point oncurve 330. The offset δ_(x) is applied from angular position φ₁ toarrive at the optimum wrap arm position φ₄, and this is the angularposition of wrap arm 22 indicated by reference numeral 314 in FIG. 5,and which also indicates the same position of wrap arm 22 illustrated inFIG. 2.

According to one aspect of the present invention, it has been founddesirable to avoid operating the wrap arm at position φ_(I) since thereis some risk, when operating in this mode, that moisture will be lostfrom the web (i.e., operation to the right of point 332 in FIG. 6). Theoperating point φ₄, indicated as the optimum operating position in FIG.6, closely corresponds to the high temperature dew-point on the fluteside of liner 11 (that side bonded to the flutes of the corrugatedmedium). This high temperature dew-point attained according toprinciples of the present invention creates the maximum amount of heatand makes available the optimum amount of moisture on the flute side ofthe liner, enhances the bond of the liner to the fluted medium.

As indicated above, it is important that the surface dew-point of liner11 be chosen as the control target. When multiple liners (includingliners of multiple single-faced board) are employed in a manufacturingprocess, the present invention automatically balances the moisturecontent of the various liner components at their highest surfacetemperatures, thus optimizing surface moisture level and surfacetemperatures, important for reliable, successful bonds usingconventional corrugated manufacturing equipment. As will be appreciatedby those skilled in the art, balancing of the moisture levels of liners(and other components) in a corrugated product greatly encourages andoftentimes is alone sufficient to ensure that a flat corrugated productwill be produced. In effect, warpage of corrugated products can beeliminated automatically and production can continue in a routine mannerwithout regard to imbalances of moisture levels in various linercomponents.

Preconditioner Control System

Turning now to FIGS. 7 and 8, operation of the preconditioner 42 will bedescribed in greater detail. The wrap arm 40 is, in the preferredembodiment, mounted for rotation about the center of cylindricalpreheater 42, between a maximum wrap position 370 and a minimum wrapposition 372. The operating positions 370, 372 lie on either side of astationary guide roller 374. In the preferred operation, wrap arm 40 isinitially moved to the minimum wrap position 372 and data collectionfrom sensor 45 is made ready.

As the wrap arm is moved from minimum position 372, to maximum position370, moisture data is collected, represented by curve 380 in FIG. 8. Theminimum wrap position 372 corresponds to position φ₀ in FIG. 8, and, ascan be seen in FIG. 8, moisture values remain relatively constant untilposition φ₁, when a rate of increase of moisture with wrap arm positionbegins. As wrap arm 40 is moved to the maximum wrap position 370, anegligible rate of increase of moisture is detected at a wrap armposition φ₂. Thereafter, with increasing movement of wrap arm 40 towardthe maximum position 370, a decrease in moisture in the web is detected(i.e., portion of curve 380 to the right of position φ₂).

The angular displacement δ_(x) between wrap arm positions φ₁ and φ₂ isdetermined, along with the arithmetic mean, position φ₃. The position φ₃is chosen as the optimum wrap arm position for operation ofpreconditioner 42. Unlike the operation of heater 24, which treats liner11, the preconditioner 42 is concerned with the uniform distribution ofmoisture throughout the thickness of the medium 31. It has been foundthat by calculating position φ₃ using the arithmetic mean of δ_(x), thenan optimum result in web 31 is achieved, both for corrugation in thesubsequent treatment of web 31, and also for bonding of the medium 31 toliner 11. The humidity sensor 45 may be any one of a number ofcommercially available humidity sensors which are employed to detecthumidity values within a paper web, as opposed to humidity sensor 27,which can be any one of a number of commercially available moisturedetectors for detecting surface moisture in paper web 11.

Preconditioning of medium 31 according to the above-described principlesachieves a pliable, unbroken fluting of the medium, even after combiningthe medium with other components of a paperboard product. Treatment ofthe medium in accordance with the present invention results in expanded,swelled, soft and pliable fibers within and throughout the medium paper.This allows for better flute formation, with consistent control of fluteheight, better absortivity for the adhesive, resulting in stronger bondsat the flute tips, and also allows for proper setting of adhesive sincean optimally preconditioned medium is provided. As a result, fluteformation is improved along with better bonding at the flute tips, withenhanced overall production speeds and improved quality values.

Electronic Control--Preheater Control Operation

Turning now to FIGS. 9a, 9b, operation of manufacturing apparatus 5 willnow be described. The flow diagram shown in FIGS. 9a, 9b pertains mostlyto operation of preheater 24, under control of electronic controller EC,although the operating system also responds to web speeds indicated byspeed indicator 68, under control of speed control circuit 69. Althoughthere are several webs that can be accommodated by the presentinvention, it should be understood that reference to web speed here isconcerned only with a liner, such as the liner 11 conditioned by heater24. As mentioned, operation of manufacturing apparatus 5 is begun withloading the rolled webs 18, and threading the webs through the system,as illustrated in FIG. 2, for example. The heaters and optional showersare brought up to operating temperatures and pressures in preparationfor a production run, indicated in FIG. 9a by block 500. Next, asindicated in decision element 502, query is made as to whether anautomatic operating mode is enabled. Generally speaking, thiscontemplates two automatic control modes, the first focusing on theoptimum positioning of wrap arm 22, and the second relating toadjustments in wrap arm position in direct proportion to the speed ofweb 11 past heater 24, as will be seen herein. If the automatic mode isnot enabled, the electronic controller EC continues to poll the systemto determine if the automatic mode has been updated.

With the automatic mode enabled, control is transferred to decisionblock 504 which tests whether the wrap arm 22 is homed to the maximumposition 310 in FIG. 5. If necessary, block 506 energizes the drivesystem (not shown) for wrap arm 22 to move it to the desired angularposition. Next, a test is conducted in decision block 508 to determineif a minimum critical web speed is maintained in the machine, and, ifnot, block 510 moves wrap arm 22 to park position 312 (see FIG. 5.

Control is then transferred to block 512, directed to a secondarycontrol of manufacturing apparatus 5. Under control of block 512, thespeed of web 11, controlled by control system 69 (see FIG. 1), ismonitored for ongoing changes during system operation. The relationbetween web speed and desired wrap position is preferably proportional,i.e., the two values are directly related. Basically, control block 512calls for greater wrap as web speed increases, and lesser wrap as webspeed decreases. It should be recognized that the wrap arm 22 can bemanually positioned by an operator with or without assistance fromsystem instrumentation. A control block 512 would perform webspeed-related adjustments to such manual wrap arm positioning if theauto mode is enabled (see block 502).

Control is then transferred to block 514 which tests whether theautomatic mode was previously initiated. If not, a test is made in block516 as to whether a splice has been made in web 11. If a splice has beenmade, the control system assumes that a recalibration is necessary.Control block 518 tests whether an optimum wrap arm operation haspreviously been achieved, and if not, control is transferred to thebeginning of the control loop, at block 502.

If an optimum mode has been previously achieved, a test is made in block520 as to whether the web speed has experienced an unacceptableperturbation, and if not, a test is made in block 522 to see whether anunacceptable perturbation in moisture has occurred. Block 520 testswhether a relatively small change in web speed has occurred. If a changeis below a preset threshold amount, then control block 512 is allowed toproceed with a ratio control of the wrap arm position, directly relatedto the web speed. If, however, block 520 detects an unacceptably largechange in speed, then control block 512 is, in effect, relieved offurther control, until a new operating point has been determined by asearch routine indicated in block 526.

Referring now to FIG. 9b, a search initiated in block 526 transferscontrol to block 528 which tests whether the moisture sensor 27 isoperational. Assuming the moisture sensor has been successfullyverified, a test is made in block 520 to determine whether a minimumcritical machine speed has been achieved, and if not, the wrap arm ismoved to the park position 312 illustrated in FIG. 5. With a minimumcritical machine speed verified, control is transferred to block 524which begins a data collection cycle, moving the wrap arm 22 to the fullwrap or maximum position 310 illustrated in FIG. 5. A test is made inblock 536 to verify that web speed is sufficiently stable, that accuratetest results will be obtained. Assuming such verification is obtained,control is then transferred to block 538 which moves wrap arm 22 fromthe maximum position 310 to the unwrapped or minimum position 308. Asmentioned above, control of wrap arm 22 by control block 538 may,optionally, require the wrap arm to be moved to the park position 312rather than to the fully wrapped minimum position 308.

In control block 540, heat and moisture data is collected as wrap arm 22is moved throughout its operational range of motion, and arepresentative example of the data obtained in control block 540 isillustrated in FIG. 6. As indicated by block 542, data collectioncontinues until the wrap arm 22 is moved to its end point (either parkposition 312 or a fully unwrapped minimum position 308). Block 544 testswhether the observed moisture values lie within a reasonable range, thephysical interpretation of which is a quick pass-fail decision as towhether the paper is (for some unusual reason) too wet or too dry.Assuming the pass-fail test is performed with a favorable outcome,control is transferred to block 546 which calculates the optimum wraparm position φ₄, using the technique described above with reference toFIG. 6. The wrap arm is then moved by control block 548 to the optimumwrap arm position φ₄. Block 549 then stores a value in memory indicatingthat optimum mode has been achieved and this data is eventually testedin decision block 518.

As indicated at the bottom of FIG. 9a, control is then transferred tothe top of the automatic control procedure, with the test then beingperformed by decision block 502. As mentioned, the optimum wrap armposition has been achieved, and is subsequently adjusted, if necessary,in control block 512, in response to a change in web speed, using a"ratio" or direct mathematical relation between web speed and wrap armposition change. Decision block 514 will test false, requiring furthertesting in decision blocks 516-522 to be performed, thus monitoring asto whether unusual perturbations in web speed or moisture change haveoccurred since the wrap arm was set to an optimum position. Ifnecessary, recalculation and determination of an updated optimum wraparm position will be required, with control being transferred to block526.

Preconditioning Heater Operation

Referring now to FIGS. 10a and 10b, operation of the preconditioningheater 42 will be described. As will be seen herein, the methodology ofcontrol is similar to that previously described for the heater 24, withthe exception of the calculation of optimum position, which has alreadybeen described with reference to FIGS. 7 and 8.

As mentioned, operation of manufacturing apparatus 5 is begun withloading the rolled webs 36, and threading the webs through the system,as illustrated in FIG. 1, for example. The heaters and optional showersare brought up to operating temperatures and pressures in preparationfor a production run, indicated in FIG. 9a by block 600. Next, asindicated in decision element 602, query is made as to whether anautomatic operating mode is enabled. Generally speaking, thiscontemplates two automatic control modes, the first focusing on theoptimum positioning of wrap arm 40, and the second relating to the speedof web 31 past heater 42, as will be seen herein. If the automatic modeis not enabled, the electronic controller EC continues to poll thesystem to determine if the automatic mode has been updated. With theautomatic mode enabled, control is transferred to decision block 604which tests whether the wrap arm 40 is homed to the minimum position 372in FIG. 7. If necessary, block 606 energizes the drive system (notshown) for wrap arm 40 to move it to the desired angular position. Next,a test is conducted in decision block 608 to determine if a minimumcritical web speed is maintained in the machine, and, if not, block 610moves wrap arm 40 to minimum position 372 (see FIG. 7). Control is thentransferred to block 612, directed to a secondary control ofmanufacturing apparatus 5. Under control of block 612, the speed of web31, controlled by control system 69, is monitored for ongoing changesduring system operation. Basically, control block 612 calls for greaterwrap as web speed increases, and lesser wrap as web speed decreases. Itshould be recognized that the wrap arm 40 can be manually positioned byan operator with or without assistance from system instrumentation. Acontrol block 612 would perform web speed-related adjustments to suchmanual wrap arm positioning if the auto mode is enabled (see block 602).

Control is then transferred to block 614 which tests whether theautomatic mode was previously initiated. If not, a test is made in block616 as to whether a splice has been made in web 11. If a splice has beenmade, the control system assumes that a recalibration is necessary.Control block 618 tests whether an optimum wrap arm operation haspreviously been achieved, and if not, control is transferred to thebeginning of the control loop, at block 602. If an optimum mode has beenpreviously achieved, a test is made in block 620 as to whether the webspeed has experienced an unacceptable perturbation, and if not, a testis made in block 622 to see whether an unacceptable perturbation inmoisture has occurred. Block 620 tests whether a relatively small changein web speed has occurred. If a change is below a preset thresholdamount, then control block 612 is allowed to proceed with a ratiocontrol of the wrap arm position, directly related to the web speed. If,however, block 620 detects an acceptably large change in speed, thencontrol block 612 is, in effect, relieved of further control, until anew operating point has been determined by a search routine indicated inblock 626.

Referring now to FIG. 9b, a search initiated in block 626 transferscontrol to block 628 which tests whether the moisture sensor 45 isoperational. Assuming the moisture sensor has been successfullyverified, a test is made in block 620 to determine whether a minimumcritical web speed has been achieved, and if not, the wrap arm is movedto the minimum position 372 illustrated in FIG. 5. With a minimumcritical machine speed verified, control is transferred to block 624which begins a data collection cycle, moving the wrap arm 40 to theminimum position 370 illustrated in FIG. 7. A test is made in block 636to verify that web speed is sufficiently stable, that accurate testresults will be obtained. Assuming such verification is obtained,control is then transferred to block 638 which moves wrap arm 40 fromthe unwrapped or minimum position 372 to the full wrapped position 370.

In control block 640, moisture data is collected as wrap arm 40 is movedthroughout its operational range of motion, and a representative exampleof the data obtained in control block 640 is illustrated in FIG. 6. Asindicated by block 642, data collection continues until the wrap arm 40is moved to its end point (fully wrapped maximum position 370). Block644 tests whether the observed moisture values lie within a reasonablerange, the physical interpretation of which is a quick pass-faildecision as to whether the paper is (for some unusual reason) too wet ortoo dry.

Assuming the pass-fail test is satisfactorily performed, control istransferred to block 646 which calculates the optimum wrap arm positionφ₃, using the technique described above with reference to FIG. 8. Wraparm 40 is then moved by control block 648 to the optimum wrap armposition φ₃. Block 646 then stores a value in memory indicating thatoptimum mode has been achieved and this data is eventually tested indecision block 618. As indicated at the bottom of FIG. 9a, control isthen transferred to the top of the automatic control procedure, with thetest then being performed by decision block 602. As mentioned, theoptimum wrap arm position has been achieved, and is subsequentlyadjusted, if necessary, in control block 612, in response to a change inweb speed, using a "ratio" or other direct mathematical relation betweenweb speed and wrap arm position change. Decision block 614 will testfalse, requiring further testing in decision blocks 616-622 to beperformed, thus monitoring as to whether unusual perturbations in webspeed or moisture change have occurred since the wrap arm was set to anoptimum position. If necessary, recalculation and determination of anupdated optimum wrap arm position will be required, with control beingtransferred to block 626.

With the present invention, the controls described above with referenceto FIG. 2 are also employed in the double-backer system described abovewith reference to FIGS. 3a and 3b. More specifically, the controlsdescribed above with reference to FIG. 1 are identically employed forthe double-backer inner board 131 and double-backer outer board 153 ofFIG. 3a. Further, these same controls are employed for the bonding ofliner 121 to the double-backer inner board 131.

From the foregoing, it will be appreciated that the invention provides anovel and improved corrugation system. The invention is not limited tothe particular embodiment described above or to any particularembodiment. In particular, the above mentioned "electronic controller"may be, but is not limited to being, an electronic or otherwiseautomated controller, a processor, a computer or a logical operator.Also, the above-mentioned "board" may be, but is not limited to beingboard, paper or other pulpy material.

Terms such as "horizontal," "vertical," etc. are used herein only todescribe the orientation of the various components relative to oneanother, when the invention is in an upright position as shown in thedrawings. It should be understood that the invention may be operated invarious different orientations, and the use of these terms is notintended to imply otherwise, nor to limit the description or claims toan invention disposed in a particular orientation.

What is claimed is:
 1. A method for preparing a paper web for adhesivejoinder, comprising the steps of:providing a paper web having first andsecond opposed major surfaces and containing moisture; providing heatingmeans with a curved outer heated surface; providing a wrap arm forwrapping the paper web across the heating means, with the wrap armmovable between first and second positions so as to bring greater andlesser portions of the paper web in contact with the heating means;moving the wrap arm between said first and said second positions so asto bring a changing amount of the first surface of the paper web incontact with the heating means; sensing, for the different positions ofthe wrap arm, the surface moisture carried by the paper web at the firstsurface and the temperature of the paper web at the first surface;determining a low temperature wrap arm position at which a rate ofincrease of surface moisture increases; determining a high temperaturewrap arm position at which a rate of increase of surface temperature isnegligible; determining an offset comprising the difference between thelow temperature wrap arm position and the high temperature wrap armposition; determining a high moisture wrap arm position at which a rateof increase of surface moisture is negligible; determining a desiredoperating position of the wrap arm by adjusting the high moisture wraparm position toward the low temperature wrap arm position by an amountcorresponding to the offset; and moving the wrap arm to the desiredoperating position.
 2. The method of claim 1 wherein the wrap arm ismoved continuously between said first and said second positions.
 3. Themethod of claim 1 wherein the wrap arm is moved from a first position ofgreater wrap to a second position of lesser wrap.
 4. The method of claim1 wherein the second major surface of the paper web contacts the heatedsurface and the surface moisture of the paper web is sensed at the firstmajor surface of the paper web.
 5. The method of claim 1 furthercomprising the steps of:conveying the paper web across the heatedsurface; observing the speed of the paper web across the heated surface;and adjusting the wrap arm according to the speed of the paper web. 6.The method of claim 5 further wherein the step of adjusting the wrap armaccording to the speed of the paper web comprises the step of moving thewrap arm toward the high temperature wrap arm position as the speed ofthe paper web increases.
 7. The method of claim 5 further wherein thestep of adjusting the wrap arm according to the speed of the paper webcomprises the step of moving the wrap arm toward the low temperaturewrap arm position as the speed of the paper web decreases.
 8. A methodfor preparing a paper web for corrugation, comprising the stepsof:providing a paper web having first and second opposed major surfacesand containing moisture; providing heating means with a curved outerheated surface; providing a wrap arm for wrapping the paper web acrossthe heating means, with the wrap arm movable between maximum and minimumpositions so as to bring greater and lesser portions of the paper web incontact with the heating means; moving the wrap arm between a series ofdifferent positions, between said maximum and said minimum positions soas to bring a changing amount of the first surface of the paper web incontact with the heating means; sensing, for the different positions ofthe wrap arm, the moisture of the paper web; determining a low moisturewrap arm position at which a rate of increase of moisture increases;determining a high moisture wrap arm position at which a rate ofincrease of web moisture is negligible; determining an offset comprisingone-half of the difference between the low moisture wrap arm positionand the high moisture wrap arm position; determining a desired operatingposition of the wrap arm by adjusting the high moisture wrap armposition toward the low moisture wrap arm position by an amountcorresponding to the offset; and moving the wrap arm to the desiredoperating position.
 9. The method of claim 8 wherein the wrap arm ismoved continuously between said first and said second positions.
 10. Themethod of claim 8 wherein the wrap arm is moved from a first position oflesser wrap to a second position of greater wrap.
 11. The method ofclaim 8 wherein the second major surface of the paper web contacts theheated surface and the moisture of the paper web is sensed at the firstmajor surface of the paper web.
 12. The method of claim 8 furthercomprising the steps of:conveying the paper web across the heatedsurface; observing the speed of the paper web across the heated surface;and adjusting the wrap arm according to the speed of the paper web. 13.The method of claim 12 further wherein the step of adjusting the wraparm according to the speed of the paper web comprises the step of movingthe wrap arm toward the high temperature wrap arm position as the speedof the paper web increases.
 14. The method of claim 12 further whereinthe step of adjusting the wrap arm according to the speed of the paperweb comprises the step of moving the wrap arm toward the low temperaturewrap arm position as the speed of the paper web decreases.
 15. A methodof joining a paper liner to a medium comprising a corrugated paper web,comprising the steps of:a) forming the liner from a paper web inpreparation for adhesive joinder to the medium, comprising the stepsof:providing a paper web having first and second opposed major surfacesand containing moisture; providing heating means with a curved outerheated surface; providing a liner wrap arm for wrapping the paper webacross the heating means, with the liner wrap arm movable between firstand second positions so as to bring greater and lesser portions of thepaper web in contact with the heating means; moving the liner wrap armbetween said first and said second positions so as to bring a changingamount of the first surface of the paper web in contact with the heatingmeans; sensing, for the different positions of the liner wrap arm, thesurface moisture carried by the paper web at the first surface and thetemperature of the paper web at the first surface; determining a lowtemperature liner wrap arm position at which a rate of increase ofsurface moisture increases; determining a high temperature liner wraparm position at which a rate of increase of surface temperature isnegligible; determining an offset comprising the difference between thelow temperature liner wrap arm position and the high temperature linerwrap arm position; determining a high moisture liner wrap arm positionat which a rate of increase of surface moisture is negligible;determining a desired operating position of the liner wrap arm byadjusting the high moisture liner wrap arm position toward the lowtemperature liner wrap arm position by an amount corresponding to theoffset; and moving the liner wrap arm to the desired operating position;b) forming the medium from another paper web in preparation for adhesivejoinder to the liner, comprising the steps of:providing another paperweb having first and second opposed major surfaces and containingmoisture; providing a medium heater with a curved outer heated surface;providing a medium wrap arm for wrapping the paper web across theheating means, with the medium wrap arm movable between maximum andminimum positions so as to bring greater and lesser portions of thepaper web in contact with the medium heater; moving the medium wrap armbetween a series of different positions, between said maximum and saidminimum positions so as to bring a changing amount of the first surfaceof the paper web in contact with the medium heater; sensing, for thedifferent positions of the medium wrap arm, the moisture of the paperweb; determining a low moisture medium wrap arm position at which a rateof increase of moisture increases; determining a high moisture mediumwrap arm position at which a rate of increase of web moisture isnegligible; determining an offset comprising one-half of the differencebetween the low moisture medium wrap arm position and the high moisturemedium wrap arm position; determining a desired operating position ofthe medium wrap arm by adjusting the high moisture medium wrap armposition toward the low moisture medium wrap arm position by an amountcorresponding to the offset; and moving the medium wrap arm to thedesired operating position; c) coating one of said liner and said mediumwith an adhesive; and pressing said liner and said medium together. 16.The method of claim 15 wherein the liner wrap arm and the medium wraparm are moved continuously between their respective said first and saidsecond positions.
 17. The method of claim 15 wherein the liner wrap armis moved from a first position of greater wrap to a second position oflesser wrap.
 18. The method of claim 15 wherein the medium wrap arm ismoved from a first position of lesser wrap to a second position ofgreater wrap.
 19. The method of claim 15 wherein the second majorsurface of the liner contacts the heated surface of the liner heater andthe surface moisture of the paper web is sensed at the first majorsurface of the liner.
 20. The method of claim 15 further comprising thesteps of:conveying the liner across the heated surface; observing thespeed of the liner across the heated surface of the liner heater;adjusting the liner wrap arm according to the speed of the liner. 21.The method of claim 20 further wherein the step of adjusting the linerwrap arm according to the speed of the liner comprises the step ofmoving the liner toward the high temperature liner wrap arm position asthe speed of the liner increases.
 22. The method of claim 20 furtherwherein the step of adjusting the liner wrap arm according to the speedof the liner comprises the step of moving the liner toward the lowtemperature liner wrap arm position as the speed of the liner decreases.23. The method of claim 15 wherein the medium wrap arm is moved from afirst position of lesser wrap to a second position of greater wrap. 24.The method of claim 15 wherein the second major surface of the mediumcontacts the heated surface of the medium heater and the surfacemoisture of the medium is sensed at the first major surface of themedium.
 25. The method of claim 15 further comprising the stepsof:conveying the medium across the heated surface of the medium heater;observing the speed of the medium across the heated surface of themedium heater; adjusting the medium wrap arm according to the speed ofthe medium.
 26. The method of claim 20 further wherein the step ofadjusting the medium wrap arm according to the speed of the mediumcomprises the step of moving the medium wrap arm toward the hightemperature liner wrap arm position as the speed of the mediumincreases.
 27. The method of claim 20 further wherein the step ofadjusting the medium wrap arm according to the speed of the mediumcomprises the step of moving the medium wrap arm toward the lowtemperature medium wrap arm position as the speed of the mediumdecreases.
 28. A method of making a double-wall corrugated board,comprising the steps of:a) forming the liner from a paper web inpreparation for adhesive joinder to the medium, comprising the stepsof:providing a paper web having first and second opposed major surfacesand containing moisture; providing heating means with a curved outerheated surface; providing a liner wrap arm for wrapping the paper webacross the heating means, with the liner wrap arm movable between firstand second positions so as to bring greater and lesser portions of thepaper web in contact with the heating means; moving the liner wrap armbetween said first and said second positions so as to bring a changingamount of the first surface of the paper web in contact with the heatingmeans; sensing, for the different positions of the liner wrap arm, thesurface moisture carried by the paper web at the first surface and thetemperature of the paper web at the first surface; determining a lowtemperature liner wrap arm position at which a rate of increase ofsurface moisture increases; determining a high temperature liner wraparm position at which a rate of increase of surface temperature isnegligible; determining an offset comprising the difference between thelow temperature liner wrap arm position and the high temperature linerwrap arm position; determining a high moisture liner wrap arm positionat which a rate of increase of surface moisture is negligible;determining a desired operating position of the liner wrap arm byadjusting the high moisture liner wrap arm position toward the lowtemperature liner wrap arm position by an amount corresponding to theoffset; and moving the liner wrap arm to the desired operating position;b) forming the medium from another paper web in preparation for adhesivejoinder to the liner, comprising the steps of:providing another paperweb having first and second opposed major surfaces and containingmoisture; providing a medium heater with a curved outer heated surface;providing a medium wrap arm for wrapping the paper web across theheating means, with the medium wrap arm movable between maximum andminimum positions so as to bring greater and lesser portions of thepaper web in contact with the medium heater; moving the medium wrap armbetween a series of different positions, between said maximum and saidminimum positions so as to bring a changing amount of the first surfaceof the paper web in contact with the medium heater; sensing, for thedifferent positions of the medium wrap arm, the moisture of the paperweb; determining a low moisture medium wrap arm position at which a rateof increase of moisture increases; determining a high moisture mediumwrap arm position at which a rate of increase of web moisture isnegligible; determining an offset comprising one-half of the differencebetween the low moisture medium wrap arm position and the high moisturemedium wrap arm position; determining a desired operating position ofthe medium wrap arm by adjusting the high moisture medium wrap armposition toward the low moisture medium wrap arm position by an amountcorresponding to the offset; and moving the medium wrap arm to thedesired operating position; c) coating one of said liner and said mediumwith an adhesive; d) pressing said liner and said medium together toform a first single-faced board; e) repeating said steps a) through d)to form a second single-faced board; f) repeating said step a) to forman other liner; g) coating said first and said second single-facedboards with an adhesive; h) pressing said other liner and said first andsaid second single-faced boards together to form said double-wallcorrugated board.
 29. The method of claim 28 wherein said first and saidsecond single-faced boards are pressed together and the first singlefaced board is then pressed into contact with said other liner.
 30. Themethod of claim 29 further comprising preparing the first single facedboard according to the following steps:providing board heating meanswith a curved outer heated surface; providing a wrap arm for wrappingthe first single-faced board across the board heating means, with thewrap arm movable between first and second positions so as to bringgreater and lesser portions of the first single-faced board in contactwith the heating means; moving the liner wrap arm between said first andsaid second positions so as to bring a changing amount of the firstsingle-faced board in contact with the board heating means; sensing, forthe different positions of the wrap arm, the temperature of and surfacemoisture carried by the liner of the first single-faced board;determining a low temperature wrap arm position at which a rate ofincrease of surface moisture increases; determining a high temperaturewrap arm position at which a rate of increase of surface temperature isnegligible; determining an offset comprising the difference between thelow temperature wrap arm position and the high temperature wrap armposition; determining a high moisture wrap arm position at which a rateof increase of surface moisture is negligible; determining a desiredoperating position of the wrap arm by adjusting the high moisture wraparm position toward the low temperature wrap arm position by an amountcorresponding to the offset; and moving the wrap arm to the desiredoperating position; and passing the first single-faced board past theboard heating means to prepare the liner of the first single-faced boardfor joinder to the second single-faced board.
 31. The method of claim 30further comprising preparing the second single faced board according tothe following steps:providing a heater with a curved outer heatedsurface; providing a wrap arm for wrapping the second single faced boardacross the heating means, with the wrap arm movable between maximum andminimum positions so as to bring greater and lesser portions of thesecond single faced board in contact with the heater; moving the wraparm between a series of different positions, between said maximum andsaid minimum positions so as to bring a changing amount of a firstsurface of the second single-faced board in contact with the heater;sensing, for the different positions of the wrap arm, the moisture ofthe second single faced board; determining a low moisture wrap armposition at which a rate of increase of sensed moisture increases;determining a high moisture wrap arm position at which a rate ofincrease of sensed moisture is negligible; determining an offsetcomprising one-half of the difference between the low moisture wrap armposition and the high moisture wrap arm position; determining a desiredoperating position of the wrap arm by adjusting the high moisture wraparm position toward the low moisture wrap arm position by an amountcorresponding to the offset; and moving the wrap arm to the desiredoperating position; and passing the second single-faced board past theheater to prepare the medium of the second single-faced board forjoinder to the first single-faced board.